The ribosomal P protein antigens are perhaps the only specific protein antigens in human and murine SLE about which the structure, function, epitopes, and amino acid sequences are known. Using the P/anti-P antigen/antibody systems, the following questions will be addressed: a) Are the P protein antigens in patients' cells normal? The primary sequence of the P proteins will be analyzed by recombinant DNA techniques and possible environmental alterations studied by two-dimensional gel electrophoresis. The effect of phosphorylation of the major epitope on autoantibody binding will be measured. b) Can unmodified P proteins stimulate and drive anti-P production in MRL/lpr and BALB/c mice? Mice will be immunized with mouse whole ribosomes and the antibody response to all ribosomal proteins analyzed by immunoblotting and anti-P levels assayed by ELISA. c) Are T cells involved in antibody production and can a T cell antigen be defined? In vitro proliferation and expression of activation antigens (Tac, Ia, MRL3) will be studied in peripheral T cells after exposure to P proteins and several possible manipulations (IL-2 supplementation, removal of T suppressor cells). Since only 15% of MRL mice produce anti-P, the role of T cells in vivo can be tested by adoptive transfer of T and B cells in anti-P positive and negative mice. d) Can anti-P antibodies be specifically suppressed in MRL mice? MRL mice will be injected with either peptide-IgG2a conjugates or P protein-polyethylene glycol conjugates at the age of 3 months and anti-P antibodies serially measured by the ELISA. e) How diverse are anti-P and anti-Sm antibodies at the genetic level and are they derived from a unique "autoimmune" subset of B cells? Monoclonal antibodies will be made from the spleens of MRL mice positive for both anti- Sm and anti-P, RNA will be isolated and sequenced. To develop safe forms of immunotherapy, it is important to understand whether autoantibody production is antigen-driven and if so, why? ((a) and (b) above). If autoantibodies are driven by antigen, then suppressive therapy ((d) above) is likely to work. If T cells are involved ((c) above), then anti-clonotypic therapy can be used. The tools are available for exploring the diversity of autoantibody production at the genetic level ((e above). Defining the genes involved in autoantibodies against the P and Sm antigens may lead to fundamental insights regarding B cell subsets involved in autoimmunity.